Wireless communication systems are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, 3GPP LTE systems, Orthogonal FDMA (OFDMA) systems, Single-Carrier FDMA (SC-FDMA) systems, etc.
In wireless communication systems access terminals (referred to as mobile stations, handsets, mobile devices, and/or user terminals) receive signals from fixed position access points (also referred to as base stations, Node-B, cell sites or cells) that support communication links or service within particular geographic regions adjacent to or surrounding the access point. In order to aid in providing coverage, each cell may be sub-divided into multiple sectors, each corresponding to a smaller service area or geographic region. An array or series of access points placed adjacent to each other can form a communication system capable of servicing a number of system users, over a larger region.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless access terminals. Each access terminal may communicate with one or more access points via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the access points to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the access points. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
Each access terminal can monitor a control channel that may be used to exchange messages between the access terminal and the access point. The control channel is used to transmit system/overhead messages, whereas traffic channels are typically used for substantive communication (e.g., voice and data) to and from the access terminal. For example, the control channel can be used to establish traffic channels, control power levels, and the like, as is known in the art.
Because the access terminals are typically battery operated, power conservation is emphasized in the system design. Accordingly, access terminals can enter into sleep modes and periodically awaken to monitor the control channel for messages/paging directed to the access terminal. During sleep modes, component(s) within the access terminal may experience drifts. These drifts may be characterized as uncontrolled variations in the performance of components in the Access Terminal. For example, an oscillator used as a frequency reference in the access terminal may provide a clock signal which experiences time and/or frequency variations. Component drift can adversely affect the functionality and/or performance of the access terminal. Moreover, this timing/frequency drift may also affect the performance of other users in the Uplink (UL) by violating the time/frequency orthogonality across users.
Accordingly, it is desirable to compensate for component drift in order to mitigate potentially adverse effects on the communication system.